One type of transistor known in the art is a Schottky-barrier metal oxide semiconductor field effect transistor (“Schottky-barrier MOSFET” or “SB-MOS). As shown in FIG. 1, the SB-MOS device 100 comprises a semiconductor substrate 110 in which a source electrode 120 and a drain electrode 125 are formed, separated by a channel region 140 having channel dopants. The channel region 140 is the current-carrying region of the substrate 110. For purposes of the present invention, the channel region 140 in the semiconductor substrate 110 extends vertically below the gate insulator 150 to a boundary approximately aligned with the bottom edge of the source 120 and bottom edge of the drain 125 electrodes. The channel dopants typically have a maximum dopant concentration 115, which is typically below the source 120 and drain 125 electrodes, and thus outside of the channel region 140.
For a SB-MOS device at least one of the source 120 or the drain 125 contacts is composed partially or fully of a metal silicide. Because at least one of the source 120 or the drain 125 contacts is composed in part of a metal, they form Schottky or Schottky-like contacts with the substrate 110 and the channel region 140. A Schottky contact is defined as a contact formed by the intimate contact between a metal and a semiconductor, and a Schottky-like contact is defined as a contact formed by the close proximity of a semiconductor and a metal. The Schottky contacts or Schottky-like contacts or junctions 130, 135 may be provided by forming the source 120 or the drain 125 from a metal silicide. The channel length is defined as the distance from the source 120 contact to the drain 125 contact, laterally across the channel region 140.
The Schottky or Schottky-like contacts or junctions 130, 135 are located in an area adjacent to the channel region 140 formed between the source 120 and drain 125. An insulating layer 150 is located on top of the channel region 140. The insulating layer 150 is composed of a material such as silicon dioxide. The channel region 140 extends vertically from the insulating layer 150 to the bottom of the source 120 and drain 125 electrodes. A gate electrode 160 is positioned on top of the insulating layer 150, and a thin insulating layer 170 surrounds the gate electrode 160. The thin insulating layer 170 is also known as the spacer. The gate electrode 160 may be doped poly silicon. The source 120 and drain 125 electrodes may extend laterally below the spacer 170 and gate electrode 160. A field oxide 190 electrically isolates devices from one another. An exemplary Schottky-barrier device is disclosed in Spinnaker's U.S. Pat. No. 6,303,479.
There is a need in the industry for a SB-MOS fabrication method that provides a SB-MOS device with improved performance, manufacturability and cost benefits.